Qi Dai1, Robert S. Sandler2, Elizabeth L. Barry3, Robert W. Summers4, Maria V. Grau5, and
John A. Baron2,5,6
High calcium consumption may confer a reduced risk of colorectal cancer.1,2 Dai and colleagues3 recently reported in a case-control study that intake of calcium may be associated with a decreased risk of colorectal adenoma only when the dietary calcium:magnesium intake ratio is low. This finding provides one possible interpretation for inconsistencies in previous studies of the association of calcium intake with risk of colorectal neoplasia.4
Belonging to the same family in the periodic table, calcium (Ca2+) and magnesium (Mg2+) share the same homeostatic control system and have the potential to antagonize each other physiologically.5 A high calcium intake reduces absorption of both magnesium and calcium,6 whereas moderate magnesium deprivation results in negative magnesium balance but increased calcium retention7. Due to the potential competition between magnesium and calcium, we hypothesized that the dietary calcium:magnesium ratio may modify the effects of calcium supplementation on colorectal carcinogenesis.
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